The present invention relates to an ultra thin type rolling bearing for use in an industrial robot, a machine tool, medical equipment or the like and a cage for such a rolling bearing.
FIG. 8 shows a CT scanner, an example of one kind of medical equipment. As shown, in the CT scanner, an X ray generated by an X ray tube assembly 20 is directed upon an object 23 through a wedge filter 21 to equalize the intensity distribution and a slit 22 to restrict the intensity distribution. The X ray passed through the object 23 is received by a detector 24, converted into an electrical signal and transferred to a computer which is not shown. Elements such as the X ray tube assembly 20, wedge filter 21, slit 22 and detector 24 are mounted on an approximately cylindrical, rotary pedestal 27 supported rotatably around a stationary pedestal 26 through a bearing 25, and driven to rotate by the rotary pedestal 27 around the object 23. In the CT scanner, the rotating movement around the object 23 of the X ray tube assembly 20 and the detector 24 opposing to each other results in projection data covering all the angles at every point within a cross section of the object 23 to be examined, and a cross sectional image is obtained based on these pieces of data using a pre-programmed reconstruction program.
In the CT scanner, the inner circumferential surface of the stationary pedestal 26 has a large opening to let the object 23 therein (approximately 1 m in diameter), and therefore a so-called ultra thin type rolling bearing having a cross section significantly small relative to the diameter is used for the bearing portion 25 between stationary pedestal 26 and rotary pedestal 27. Among such ultra thin type rolling bearings, a so-called combination angular contact ball bearing formed by combining two angular contact ball bearings X and Y as shown in FIG. 9 is used, particularly when such a bearing is used at a high rotating speed of about 120 rpm or higher. The combination angular contact ball bearing as shown is a so-called back-to-back arrangement having the two angular contact ball bearings X and Y with their back faces (faces which can receive the thrust load) in contact with each other, and pressurizing force is allowed to act upon in the direction in which the outer ring 31 (outer member) of one bearing X and the inner ring 32 (inner member) of the other bearing Y face each other, so that appropriate preload is applied to the inside of the bearings for use.
According to the conventional device, the outer annular body 33 is threadedly secured to one pedestal (the rotary pedestal 27, for example), and inner annular body 34 is threadedly secured to the other pedestal (the stationary pedestal 26, for example). Each outer rings 31 of the two bearings X and Y is engaged to the inner circumferential surface of the outer annular body 33, while each inner ring 32 of the two bearings X and Y is engaged to the outer circumferential surface of the inner annular body 34, so that the rotary pedestal 27 is rotatably supported. A presser member 36 is secured to each of one end side of inner annular body 34 and the other side of outer annular body 33, using a fastening screw 35, and the presser members 36 press the end surfaces of the outer ring 31 and inner ring 32, and the end surfaces on the opposite side are received by shoulder portions 33a and 34a provided at the outer annular body 33 and inner annular body 34, respectively, so that preload is applied to the inside of the bearings.
In the conventional ultra thin type rolling bearing for the CT scanner as described above, a cage 4xe2x80x2 of resin is used. The resin cage 4xe2x80x2 is of a separate type cage formed into an annular shape by connecting a plurality of segments 40xe2x80x2 having a circular cross section as shown in FIG. 10(a), and in the conventional device, recessed or raised engaging portion 44axe2x80x2, 44bxe2x80x2 are formed at the ends of each segment 40xe2x80x2 as described in FIG. 10(b), and the recessed or raised engaging portion 44axe2x80x2, 44bxe2x80x2 is engaged to raised or recessed engaging portion 44bxe2x80x2, 44axe2x80x2 at the segment end to be coupled therewith, so that they are engaged with each other in the circumferential direction to couple each segment 40xe2x80x2.
The conventional ultra thin type rolling bearing for the CT scanner is assembled with a large number of parts including the outer and inner annular bodies 33 and 34, presser members 36, in addition to the bearing parts such as the outer rings 31 and inner rings 32 as described above. Since such a large number of parts are necessary, the precision of each part would be added up to lower the entire precision, and therefore, strict precision control is demanded for each part. Furthermore, since the bearing portion is extremely thin, if the deviation from circular is even slightly deviated than allowed for the inner and outer annular bodies, the bearing ring bends along the shape, which adversely affects the performance of the bearing, and therefore the outer and inner rings should also be finished with high precision. As a result, the part and assembly cost for the conventional bearings has been increased and there is a strong demand for cost reduction.
Also in the conventional resin cage, segments are coupled with their recessed and raised engaging portions as described above, but the engagement between the recessed and raised engaging portions can be loose depending upon the formation error at the time of forming the resin. In this case, individual segments tend to shift toward the inner and outer diameter sides, which may cause oscillation when the rotating speed is increased. In order to solve this problem, the recessed and raised engaging portions should be formed with high precision but realizing this requires much work including correction of forming molds, which pushes up the cost.
It is therefore an object of the present invention to reduce the number of parts and reduce the manufacturing cost as a result. Another object of the present invention is to securely and less costly prevent the coupling portions of a separate type cage from being shifted in the circumferential and radial directions.
In order to achieve the above-described objects, an ultra thin type rolling bearing according to the present invention includes an outer member having a double row raceway surface in which a rolling element rotates at its inner circumferential surface, an inner member provided on the inner circumferential side of the outer member, formed of an annular member and an engaging member engaged at the outer circumference of the annular member with an axial clearance with respect to the annular member, and provided with raceway surfaces in which rolling elements rotate at respective outer circumferential surfaces of the annular member and the engaging member, rolling elements inserted in two rows between the outer and inner members and having a diameter whose ratio relative to a pitch circle diameter is 0.03 or less, and a preloading means for pressurizing the engaging member to reduce the axial clearance for preloading.
Alternatively, the ultra thin type rolling bearing may include an outer member having a double row raceway surface in which a rolling element rotates at its inner circumferential surface, an inner member provided on the inner circumferential side of the outer member, formed of an annular member and a pair of engaging members engaged at the outer circumference of the annular member with an axial clearance therebetween, and provided with raceway surfaces in which rolling elements rotate at respective outer circumferential surfaces of both engaging members, rolling elements inserted in two rows between the outer and inner members and having a diameter whose ratio relative to a pitch circle diameter is 0.03 or less, and a preloading means for pressurizing one engaging member to reduce the axial clearance for preloading.
An ultra thin type rolling bearing according to the present invention may include an outer member, an inner member provided on the inner circumferential side of the outer member, a plurality of rolling elements inserted between the inner member and the outer member and having a diameter whose ratio relative to a pitch circle diameter is 0.03 or less, and a cage having a plurality of pockets each retaining a rolling element, formed into an annular shape by coupling a plurality of resin segments, and provided with engaging portions at coupling portions with adjacent segments to matingly engage the coupling portions of the corresponding side segments in the circumferential and radial directions.
In the case, the circumferential engaging portions to matingly engage the coupling portions of the corresponding side segments in the circumferential direction and radial engaging portions to matingly engage said coupling portions in the radial direction may be discretely or integrally provided.
One of the above described outer and inner members may be secured at the rotary pedestal of a CT scanner rotating around an object, and the other may be secured at the stationary pedestal of the device.
A cage for an ultra thin type rolling bearing according to the present invention is used in an ultra thin type rolling bearing in which the ratio of a rolling element diameter and a pitch circle diameter is 0.03 or less. The cage has a plurality of pockets to retain rolling elements. The cage is formed into an annular shape by coupling a plurality of resin segments and is provided with engaging portions at coupling portions with adjacent segments to matingly engage the coupling portions of the corresponding side segments in the circumferential and axial directions.
Also in this case, the circumferential engaging portions to matingly engage the coupling portions of the corresponding side segments in the circumferential direction and the radial engaging portions to matingly engage said coupling portions in the radial direction may be discretely or integrally provided.
The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.